1) Field of the Invention
This invention relates to a magnetoresistive sensor, a thin film magnetic head, a magnetic head device, and a magnetic disk drive device.
2) Related Art Statement
With recent downsizing of a magnetic disk drive device, a thin film magnetic head having a magnetoresistive sensor which takes advantage of its magnetoresistive effect, has been employed as a magnetic converter suitable for reading data recorded in a magnetic recording medium in a high recording density because its output is not influenced by the relative velocity for the magnetic recording medium.
Conventionally, a reading element with an anisotropic magnetoresistive effective film (hereinafter, called as an xe2x80x9cAMR filmxe2x80x9d) made of permalloy or the like is employed as the above magnetic converter, but recently, a reading element with a giant magnetoresistive effective film (hereinafter, called as a xe2x80x9cGMR filmxe2x80x9d), particularly a spin-valve film structure is mainly used. A magnetoresistive sensor with the spin-valve film structure is disclosed in Japanese Nonexamined Patent Publication Kokai Hei 4-358301 and xe2x80x9cIEEE TRANSACTION ON MAGNETICS, Vol. 30, No. 6xe2x80x9d, November, 1994. The spin-valve film structure has an underfilm, a first ferromagnetic film (free layer), a conductive film, an anti-ferromagnetic film and a second ferromagnetic film.
The first ferromagnetic film is made of a metallic film or an alloy film which have their respective face centered cubic crystal structure, and concretely, made of a stacked film composed of a NiFe film and a CoFe film.
The underfilm is made of the material which is selected in light of obtaining a high magnetoresistive effective converting ratio (hereinafter, called as a xe2x80x9cMR converting ratioxe2x80x9d) through its large (111) plane orientation, small diffusion for the first ferromagnetic film, and its large corrosion resistance. Concretely, in the case of making the first ferromagnetic film of the above stacked film, the underfilm is preferably made of a metallic film such as a Ta film, a Nb film, a Zr film and a Hf film.
The second ferromagnetic film is stacked on and bonded to the antiferromagnetic film with exchange interaction, and thus, its magnetization is pinned in one direction. In this specification, the pinned second ferromagnetic film is often called as a xe2x80x9cpinned layerxe2x80x9d. The conductive film is formed between the first and the second ferromagnetic films.
When an external magnetic field is applied to the spin-valve film structure, the magnetization of the first ferromagnetic film is rotated by the external magnetic field. The resistance of the spin-valve film structure is determined by the relative angle of the magnetization of the first ferromagnetic film for the magnetization of the second ferromagnetic film. The spin-valve film structure has its maximum resistance when the magnetization direction of the first ferromagnetic film is opposite to that of the second ferromagnetic film, and has its minimum resistance when the magnetization direction of the first ferromagnetic film is the same as that of the second ferromagnetic film. Then, the external magnetic field is detected from the resistance change.
However, when the underfilm is made of the above Ta film, Nb film, Zr film, Hf film or the like, a large MR converting ratio can not be realized in spite of the above appropriate material selection for the first ferromagnetic film. Concretely, the spin-valve film structure having a Ta underfilm and a NiFe/CoFe stacking first ferromagnetic film has only 7-8% MR converting ratio.
It is an object of the present invention to provide a magnetoresistive sensor capable of realizing a MR converting ratio of 10% or over.
It is another object of the present invention to provide a thin film magnetic head, a magnetic head device and a magnetic disk drive device having the above magnetoresistive sensor.
For solving the above matter, a magnetoresistive sensor according to the present invention has a spin-valve film structure which includes an underfilm, a first ferromagnetic film, a conductive film, a second ferromagnetic film, an antiferromagnetic film and a protective film.
One surface of the first ferromagnetic film is adjacent to the one surface of the underfilm, and the one surface of the conductive film is adjacent to the other surface of the first ferromagnetic film. One surface of the second ferromagnetic film is adjacent to the other surface of the conductive film. One surface of the antiferromagnetic film adjacent to the other surface of the second ferromagnetic film, and thus, the antiferromagnetic film is bonded to the second ferromagnetic film with exchange interaction. One surface of the protective film is adjacent to the other surface of the antiferromagnetic film. That is, the underfilm, the first ferromagnetic film, the conductive film, the second ferromagnetic film, the antiferromagnetic film and the protective film are stacked in turn.
In the above magnetoresistive sensor of the present invention, the second ferromagnetic film is adjacent to the antiferromagnetic film, and magnetized in one direction through the exchange interaction. In this case, the magnetization of the first ferromagnetic film is rotated by the applied external magnetic field. The resistance of the spin-valve film structure is determined by the relative angle of the magnetization direction of the first ferromagnetic film for that of the second ferromagnetic film. The external magnetic field is detected by the sense current change corresponding to the resistance change.
The underfilm has a face centered cubic crystal structure, and is oriented in the (111) plane direction. Then, the distance between the adjacent (111) planes of the spin-valve film structure except the antiferromagnetic film is within 0.2050-0.2064 nm. As a result, the spin-valve film structure can have a MR converting ratio of 10% or over.
The spin-valve film structure has the protective film on the antiferromagnetic film as well as a conventional one. The protective film may have the same crystal structure and be made of the same material as the underfilm.
The magnetoresistive sensor of the present invention may have another embodiment in which the antiferromagnetic film is positioned at the lower side of the spin-valve film structure. In this case, the one surface of the antiferromagnetic film is adjacent to the one surface of the underfilm. Then, the one surface of the second ferromagnetic film is adjacent to the other surface of the antiferromagnetic film, and thus, they are bonded each other with exchange interaction. The one surface of the conductive film is adjacent to the other surface of the second ferromagnetic film. The one surface of the first ferromagnetic film is adjacent to the other surface of the conductive film. The one surface of the protective film is adjacent to the other surface of the first ferromagnetic film. That is, the underfilm, the antiferromagnetic film, the second magnetic film, the conductive film, the first ferromagnetic film and the protective film are stacked in turn.
In this case, the underfilm also has a face centered cubic crystal structure, and is oriented in the (111) plane direction. Then, the distance between the adjacent (111) planes of the spin-valve film structure except the antiferromagnetic film is set within 0.2050-0.2064 nm. As a result, the spin-valve film structure can have a MR converting ratio of 10% or over.
A thin film magnetic head according to the present invention has a reading element composed of the above magnetoresistive sensor of the present invention, and thus, can exhibit the same operation and effect as the magnetoresistive sensor.
The thin film magnetic head may also have at least one writing element in addition to the above reading element. The writing element may be composed of a longitudinal recording inductive type electromagnetic converting element or a perpendicularly recording inductive type electromagnetic converting element. The longitudinal recording inductive type electromagnetic converting element has a first magnetic film, a second magnetic film and a gap film. The forefronts of the first and the second magnetic films are separated by the gap film, constituting a writing pole portion.
The perpendicular recording inductive type electromagnetic converting element has a first magnetic film and a second magnetic film. The second magnetic film includes a main magnetic pole to constitute a writing pole portion and a supplementary magnetic pole to magnetically combine the main magnetic pole and the first magnetic film.
This invention relates to a magnetic head device and a magnetic disk drive device having the above thin film magnetic head.